ADDITIVE MANUFACTURING (Stereolithography & Selective Laser Sintering) Introduction Additive manufacturing or 3D printing is a process of making a three-dimensional solid object of virtually any shape from a digital model. 3D printing is achieved using an additive process, where successive layers of material are laid down in different shapes. 3D printing is considered distinct from traditional machining techniques, which mostly rely on the removal of material by methods such as cutting or drilling which are subtractive processes.
The technology is used for both prototyping and distributed manufacturing in jewelry, industrial design, architecture, engineering and construction (AEC), automotive, aerospace, dental and medical industries, education, geographic information systems, civil engineering, and many other fields. The process is also known as Layered Manufacturing and Rapid Prototyping. Terminology The term additive manufacturing refers to technologies that create objects through a sequential layering process.
Objects that are manufactured additively can be used anywhere throughout the product life cycle, from pre-production (i. e. rapid prototyping) to full-scale production (i. e. rapid manufacturing), in addition to tooling applications and post-production customization. In manufacturing, and machining in particular, subtractive methods are typically coined as traditional methods. The very term subtractive manufacturing is a retronym developed in recent years to distinguish it from newer additive manufacturing techniques.
Although fabrication has included methods that are essentially “additive” for centuries (such as joining plates, sheets, forgings, and rolled work via riveting, screwing, forge welding, or newer kinds of welding), it did not include the information technology component of model-based definition. Machining (generating exact shapes with high precision) has typically been subtractive, from filing and turning to milling and grinding. General Principle
Additive manufacturing takes virtual blueprints from computer aided design (CAD) or animation modeling software and “slices” them into digital cross-sections for the machine to successively use as a guideline for printing. Depending on the machine used, material or a binding material is deposited on the build bed or platform until material/binder layering is complete and the final 3D model has been “printed. A standard data interface between CAD software and the machines is the STL file format.
An STL file approximates the shape of a part or assembly using triangular facets. Smaller facets produce a higher quality surface. STL files describe only the surface geometry of a 3D object without any representation of color, texture or other common CAD model attributes and the file format is supported by many software packages. 3D model slicing 3D model slicing To perform a print, the machine reads the design from the STL file and lays down successive layers of liquid, powder, paper or sheet material to build the model from a series of cross sections.
These layers, which correspond to the virtual cross sections from the CAD model, are joined together or automatically fused to create the final shape. Various Additive Processes Several different 3D printing processes have been invented since the late 1970s. The printers were originally large, expensive, and highly limited in what they could produce. A number of additive processes are now available. They differ in the way layers are deposited to create parts and in the materials that can be used.
Some methods melt or soften material to produce the layers, e. g. selective laser sintering (SLS) and fused deposition modeling (FDM), while others cure liquid materials using different sophisticated technologies, e. g. Stereolithography (SLA). Type| Technologies| Materials| Extrusion| Fused deposition modeling (FDM)| Thermoplastics, HDPE, eutectic metals, edible materials| Wire| Electron Beam Freeform Fabrication (EBF3)| Almost any metal alloy| Granular| Direct metal laser
sintering (DMLS)| Almost any metal alloy| | Electron beam melting (EBM)| Titanium alloys| | Selective heat sintering (SHS)| Thermoplastic powder| | Selective laser sintering (SLS)| Thermoplastics, metal powders, ceramic powders| | Plaster-based 3D printing (PP)| Plaster| Laminated| Laminated object manufacturing (LOM)| Paper, metal foil, plastic film| Light polymerized| Stereolithography (SLA)| Photopolymer| | Digital Light Processing (DLP)| Photopolymer| Stereolithography
Stereolithography (SLA or SL; also known as optical fabrication, photo-solidification, solid free-form fabrication and solid imaging) is an additive manufacturing (or 3D printing) technology used for producing models, prototypes, patterns. The term “Stereolithography” was coined in 1986 by Charles (Chuck) W. Hull, who patented it as a method and apparatus for making solid objects by successively “printing” thin layers of an ultraviolet curable material one on top of the other. Hull’s patent described a concentrated beam of ultraviolet light focused onto the surface of a vat filled with liquid photopolymer.
The light beam draws the object onto the surface of the liquid layer by layer, and using polymerization or cross-linking to create a solid, a complex process which requires automation. Stereolithography The Technology Stereolithography is an additive manufacturing process which employs a vat of liquid ultraviolet curable photopolymer “resin” and an ultraviolet laser to build parts’ layers one at a time. For each layer, the laser beam traces a cross-section of the part pattern on the surface of the liquid resin.
Exposure to the ultraviolet laser light cures and solidifies the pattern traced on the resin and joins it to the layer below. After the pattern has been traced, the SLA’s elevator platform descends by a distance equal to the thickness of a single layer, typically 0. 05 mm to 0. 15 mm (0. 002″ to 0. 006″). Then, a resin-filled blade sweeps across the cross section of the part, re-coating it with fresh material. On this new liquid surface, the subsequent layer pattern is traced, joining the previous layer. A complete 3-D part is formed by this process.
After being built, parts are immersed in a chemical bath in order to be cleaned of excess resin and are subsequently cured in an ultraviolet oven. Ups and Downs of the process: * Main highlight of this process is speed * Complex shapes are easily developed * Parts more than 2m in length can be produced * Very high resolution * Very expensive, the cost of photo-curable resin ranges from $80 to $210/li * Stereolithography machines cost $100,000 to more than $500,000 Fields of application: * Automotive * Aerospace * Sports * Medicine
* Jewelry and Artifacts Selective Laser Sintering Selective laser sintering (SLS) is an additive manufacturing technique used for the low volume production of prototype models and functional components. Selective Laser Sintering (SLS) was developed and patented by Dr. Carl Deckard and academic adviser, Dr. Joe Beaman at the University of Texas at Austin in the mid-1980s, under sponsorship of DARPA. Deckard and Beaman were involved in the resulting startup company DTM, established to design and build the Selective Laser Sintering Machines.
In 2001, 3D Systems the biggest competitor of DTM and SLS technology acquired DTM. The Technology An additive manufacturing layer technology SLS involves the use of a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal (direct metal laser sintering), ceramic, or glass powders into a mass that has a desired three-dimensional shape. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part (for example from a CAD file or scan data) on the surface of a powder bed.
After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed. Because finished part density depends on peak laser power, rather than laser duration, a SLS machine typically uses a pulsed laser. The SLS machine preheats the bulk powder material in the powder bed somewhat below its melting point, to make it easier for the laser to raise the temperature of the selected regions the rest of the way to the melting point. Selective LASER Sintering
Applications & Advantages: Some SLS machines use single-component powder, such as direct metal laser sintering. However, most SLS machines use two-component powders, typically either coated powder or a powder mixture. In single-component powders, the laser melts only the outer surface of the particles (surface melting), fusing the solid non-melted cores to each other and to the previous layer. Compared with other methods of additive manufacturing, SLS can produce parts from a relatively wide range of commercially available powder materials.
These include polymers such as nylon (neat, glass-filled, or with other fillers) or polystyrene, metals including steel, titanium, alloy mixtures, and composites and green sand. The physical process can be full melting, partial melting, or liquid-phase sintering. Depending on the material, up to 100% density can be achieved with material properties comparable to those from conventional manufacturing methods. In many cases large numbers of parts can be packed within the powder bed, allowing very high productivity. A Product of Sintering of metal The Future of Rapid Prototyping:
Various technological advancements in the field of Rapid Prototyping have led to creation of machines which can autonomously use various resources from the environment and create a replica of it. A self-replicating machine would need to have the capacity to gather energy and raw materials, process the raw materials into finished components, and then assemble them into a copy of itself. Further, for a complete self-replication, it must, from scratch, produce its smallest parts, such as bearings, connectors and delicate and intricate electronic components.
It is unlikely that this would all be contained within a single structure, but would rather be a group of cooperating machines or an automated factory that is capable of manufacturing all of the machines that comprise it. Conclusion Rapid Prototyping is the future for the next generation of design and manufacturing. We have compared Rapid Prototyping with the traditional way of design and manufacturing and found that there are many advantages with Rapid Prototyping. The key advantages highlighted are decreasing development time, minimize sustain engineering changes and increasing the number of variants of products.
Rapid prototyping is an emerging technology that promises a brighter and efficient future. It is a technology that is worth looking forward to the future, or perhaps a technology, which would be able to take over the current technology. References * ^ Lou, Alex and Grosvenor, Carol “Selective Laser Sintering, Birth of an Industry”, The University of Texas, December 07, 2012. Retrieved on March 22, 2013. * ^ Mammoth stereo lithography: Technical specifications. materialise. com * http://blog. nus. edu. sg/ * www. wikipedia. com * www. howstuffworks. com
